Decanting centrifuge for draining off water from sewage sludge

ABSTRACT

Decanting centrifuge for draining off water from sewage sludge, which centrifuge has a rotating bowl and helical walls rotating therein to scrape the sludge towards the end of the bowl to discard it. The rotating bowl has a conical entrance section in which the helical walls are provided, where the progression of the sludge through the conical section is retarded, the conical shape of the section being important to secure a gradual increase of velocity and to reduce any tendency to create turbulence.

United States Patent 1191 Bye-Jorgensen et a1. Jan. 1, 1974 [54] DECANTING CENTRIFUGE F011 DRAINING 3,268,159 8/1966 Kern 233/7 OFF WATER FROM SEWAGE SLUDGE 2,919,848 1/1960 Howe..... 233/7 J H l b k 3,275,230 9/1966 Hiller 233/7 75 Inventors: Jor en B eor ensen um e ae I g g g Larsn, Rungsted FOREIGN PATENTS OR APPLICATIONS Kyst, both of Denmark 876,531 8/1942 France 899,310 6/1962 Great Britain 233/7 Asslgneer L Kruger A/S, Copenhagen, 661,668 6/1938 Germany 233 7 Denmark [22] Filed: June 3, 1971 Primary Examiner-George I-I. Krizmanich Attorney-Arno1d Robinson [21] Appl. No.: 149,670 V T [30] Foreign Application Priority Data [57] ABSTRACT July 11, 1970 Denmark ..703019 Decanting Centrifuge for draining Off Water from i m age sludge, which centrifuge has a rotating bowl and [52] US- Cl. 233/7 helical walls rotating therein to scrape the sludge [51] Int. Cl. B041) 1/20 towards the end of the bow] to discard it, The rotating Field of Search 28 bowl has a conical entrance section in which the helical walls are provided, where the progression of the [56] References Cit d sludge through the conical section is retarded, the UNITED STATESPATENTS conical shape of the section being important to secure 2 184 59:; 12/1939 .Iahn 233/2 a gradual increase of Velocity and reduce any 2,734,681 2/1956 Schmiedel 1 233/7 dency to create turbulence- 2,766,93O 10/1956 Schmiedel 233/7 3,143,504 8/1964 Schneider 233/7 8 2 D'awmg 3,322,336 5/1967 Lohse et a1. 233/7 499,347 6/1893 Peck 233/7 The present invention relates to a decanting centrifuge for draining off water'from sewage sludge introduced into the centrifuge through or near the shaft thereof. In such centrifuges it is in some cases of considerable importance that the sludge introduced be subjected as little as possible to the risk of hitting the inner rotating surface of the centrifuge with such power that the flocks of the sludge are decomposed into such fine particles that they can only with difficulty or not at all be precipitated in the centrifuge. Furthermore, it is of importance that the inflow period in the centrifuge, i.e., the period during which the flowing sludge is accelerated to follow the rotating movement of the centrifuge, is increased inorder to avoid the undesirable effects of turbulence occurring when the sludge is rapidly progressed through the inflow portion of the centrifuge. These objectives are achieved by using a decanting centrifuge, in which the rotating bowl has a small diameter in the region where the introduction takes place, so as to restrict the free drop of the sludge to a small distance, and at the same time providing a smooth passage, such as a conus, from the narrow part of the bowl to the wider part thereof, and providing in parts of the bowl, where the diameter increases, means by which the progression of the sludge through the narrow part of the bowl is prolonged. Owing to the fact that the rotating bowl of the centrifuge is narrowed at the inlet end so that the free drop of the introduced sludge will be small, there will be more time for the sludge to be accelerated to the high velocity at which the inner surface of the remaining part of the centrifuge bowl is moving, and because of the smooth transition to those parts of the centrifuge having an increased diameter, the subsequent increase in speed is equalized. The helical walls built into the centrifuge bowl and essentially following the movement thereof serve to increase the distance which the sludge has to progress before leaving the narrower part of the centrifuge bowl, said part enlarging towards the main part of the centrifuge. Consequently, the sludge is not subjected to any violent turbulence-causing influence.

The helical wall or walls can rotate with a speed which is differing to some extent, for example by l/2 percent, from that of the centrifuge bowl. As a result the edges of the helical bodies exert a conveying effect on the sludge particles, which deposit on the inner surface of the centrifuge bowl. This conveying effect can be used for carrying the sludge to a suitable place on the centrifuge bowl, where the sludge can be ejected, for example at the other end ofthe bowl. For this purpose, the helical walls must continue through the whole or essentially the whole length of the centrifuge bowl.

The invention will be explained more detailed with reference to the accompanying drawing, on which FIG. 1 shows schematically, in a longitudinal semisection shows one embodiment, in which the deposited sludge particles are ejected at the end of the centrifuge, which is remotest from the inlet, and

FIG. 2 shows schematically a second embodiment, in which the deposited sludge particles are ejected at the end of the centrifuge, where the inlet is placed.

In the FIGS., the same number is used for an identical part wherever it occurs.

In the embodiment of FIG. I a centrifuge 10 is shown having a rotating drum 12 with a drum cylindrical portion 14 and two conically tapered end portions 16 and 18 integral with said cylindrical portion. A hollow shaft 20 fitted into the tapered end of the conical end portion 16 at the end portions point of smallest diameter 21 provides an inlet of smaller diameter than the drum cylindrical portion 14 at point 22 for the sludge to be dewatered. The sludge enters the centrifuge through the opening 24 of the hollow shaft passing on to the sloping inner surface 26 of the conical end portion 16. The inner surface 26 of end portion 16, the inner surface 28 of cylindrical portion 14 and the inner surface 30 of end portion 18 form a continuous liquid-tight drum surface. Inside the centrifuge 10, a rotating helical conveyor 32 is provided, the speed of rotation of which is small as compared with the speed of rotation of drum l2. Helical blade 34 of the conveyor is carried by a shaft 36 and extends substantially from the opening 22 adjacent the inner surface 26 for substantially the length of the centrifuge. The pitch of the helical conveyor 32 is designed to retard the flow of the sewage and at the same time guide it towards the exit 38 of the centrifuge 10, thereby allowing more time for the water to be separated from the sludge. The partially dewatered sludge leaves the centrifuge 10 at the exit 38. The separated water is drawn off in known manner through an opening 40 of the siphon arrangement 42 in shaft Another embodiment for removing the separated water and the partially dewatered sludge is shown in FIG. 2. In FIG. 2, a centrifuge is shown having a rotating liquid-tight drum 52 with a drum cylindrical portion 54 and a conically tapered end portion 56. Inner surface 58 of drum end portion 56 and inner surface 60 of drum cylindrical portion 54 form a continuous liquid-tight drum surface. Hollow shaft 20, inlet 22 of smaller diameter than drum cylindrical portion 54 and opening 24 are provided as described for the embodiment of FIG. 1. Similar to the embodiment of FIG. 1, the sludge enters the centrifuge through opening 24 and passes to the sloping inner surface of conical end portion 56 at the point of smallest diameter 61 of end portion 56. Inside centrifuge 50, similar to FIG. 1, a rotating helical conveyor 62 is provided which rotates and operates as described hereinabove for FIG. 1. Conveyor 62 and drum 52 are enclosed by a rotating bowl 64 having a cylindrical portion 66 and two conically tapered end portions 68 and 70. A continuous liquidtight bowl surface is formed by inner surfaces 74, 76 and 78 of bowl portions 68, 66 and 70, respectively. The conveyor 62 and drum 52 extend substantially from opening 22 adjacent the point of smallest diameter 61 substantially for the length of the bowl end portion 68 and bowl cylindrical portion 66. Helical conveyor blades 80 are provided on dlrum 52 in the space or compartment 82 provided between drum 52 and how] 64. The drum end portion 56 and the bowl end portion .68, and the drum cylindrical portion 54 and the bowl cylindrical portion 66 are in substantial alignment.

The sludge and water, after dropping to surface 58, are conveyed towards the drum cylindrical portion 54. The separated water leaves throughexit 84 and the par tially dewatered sludge falls into compartment 82 where it is moved by the helical conveyor blades 80 which are pitched to convey the sludge towards exit 88.

In the FIGS., casings, guard plates, packings and similar portions are well known and therefore not shown.

These parts are well known and can be chosen by one of ordinary skill in the art.

We claim:

l. A decanting centrifuge for drawing off water from sewage sludge comprising:

1. a horizontally disposed rotary drum having a drum cylindrical portion and at least one conically tapered drum end portion disposed adjacent said drum cylindrical portion, said at least one drum end portion providing an opening at one end of said drum of smaller diameter than that of said drum cylindrical portion, said drum cylindrical and said at least one drum end portion forming a continuous light-tight drum surface,;

2. means for feeding sludge into said opening and against the tapered surface of said first drum end portion at its point of smallest diameter;

3. a first helical conveyor in the interior of said rotary drum disposed to rotate separate from said rotary drum, said helical conveyor extending substantially from said at least one drum end portionthrough said drum cylindrical portion and being pitched to guide the sewage sludge and separated water in a common direction away from said opening;

4. means for removing the separated water from said rotary drum; and

5. means for removing the sewage sludge from said rotary drum.

2. A decanting centrifuge as claimed in claim 1 wherein said helical conveyor and said rotary drum rotate at different speeds.

3. A decanting centrifuge as claimed in claim 2 wherein said rotary drum comprises two conically tapered drum end portions, said drum cylindrical portion being disposed between first and second drum end portions, said drum portions forming a continuous liquidtight drum surface, and said means for removing said sewage sludge comprises a discharge unit disposed in said second drum end portion.

4. A decanting centrifuge as claimed in claim 2 wherein said means for removing the separated water is disposed in the interior of said drum where said drum cylindrical portion are joined and said second drum end portion.

5. A decanting centrifuge as claimed in claim 2, further comprising a rotating bowlabout which said rotary drum rotates, said bowl comprising conically tapered first and second bowl end portions and a bowl cylindrical portion disposed between said bowl end portions, said bowl end and cylindrical portions providing a continuous liquid-tight surface in said bowl, the diameter of said bowl end portions increasing in the direction of said bowl cylindrical portion, said bowl cylindrical portion and said drum cylindrical portion, and said bowl first end portion and said drum first end portion being substantially aligned.

6. A decanting centrifuge as claimed in claim 5 wherein said means for removing the separated water comprises a discharge exit disposed in said second bowl end portion.

7. A decanting centrifuge as claimed in claim 5 wherein said bowl and said drum are disposed so that a space is provided therebetween, and said means for removing sewage sludge comprises a second helical conveyor secured to said rotary drum and disposed in said space between said rotary drum and said bowl, said second helical conveyor being pitched to guide the sewage sludge in a direction opposite to that of said first helical conveyor.

8. means decanting centrifuge as claimed in claim 7 wherein said menas for removing sewage sludge further comprises a discharge exit disposed between the tapered surfaces of said first drum end portion and said first bowl end portion at the points of smallest diameter of said'respective end portions. 

1. A decanting centrifuge for drawing off water from sewage sludge comprising:
 1. a horizontally disposed rotary drum having a drum cylindrical portion and at least one conically tapered drum end portion disposed adjacent said drum cylindrical portion, said at least one drum end portion providing an opening at one end of said drum of smaller diameter than that of said drum cylindrical portion, said drum cylindrical and said at least one drum end portion forming a continuous light-tight drum surface,;
 2. means for feeding sludge into said opening and against the tapered surface of said first drum end portion at its point of smallest diameter;
 3. a first helical conveyor in the interior of said rotary drum disposed to rotate separate from said rotary drum, said helical conveyor extending substantially from said at least one drum end portion through said drum cylindrical portion and being pitched to guide the sewage sludge and separated water in a common direction away from said opening;
 4. means for removing the separated water from said rotary drum; and
 5. means for removing the sewage sludge from said rotary drum.
 2. means for feeding sludge into said opening and against the tapered surface of said first drum end portion at its point of smallest diameter;
 2. A decanting centrifuge as claimed in claim 1 wherein said helical conveyor and said rotary drum rotate at different speeds.
 3. a first helical conveyor in the interior of said rotary drum disposed to rotate separate from said rotary drum, said helical conveyor extending substantially from said at least one drum end portion through said drum cylindrical portion and being pitched to guide the sewage sludge and separated water in a common direction away from said opening;
 3. A decanting centrifuge as claimed in claim 2 wherein said rotary drum comprises two conically tapered drum end portions, said drum cylindrical portion being disposed between first and second drum end portions, said drum portions forming a continuous liquid-tight drum surface, and said means for removing said sewage sludge comprises a discharge unit disposed in said second drum end portion.
 4. means for removing the separated water from said rotary drum; and
 4. A decanting centrifuge as claimed in claim 2 wherein said means for removing the separated water is disposed in the interior of said drum where said drum cylindrical portion are joined and said second drum end portion.
 5. means for removing the sewage sludge from said rotary drum.
 5. A decanting centrifuge as claimed in claim 2, further comprising a rotating bowl about which said rotary drum rotates, said bowl comprising conically tapered first and second bowl end portions and a bowl cylindrical portion disposed between said bowl end portions, said bowl end and cylindrical portions providing a continuous liquid-tight surface in said bowl, the diameter of said bowl end portions increasing in the direction of said bowl cylindrical portion, said bowl cylindrical portion and said drum cylindrical portion, and said bowl first end portion and said drum first end portion being substantially aligned.
 6. A decanting centrifuge as claimed in claim 5 wherein said means for removing the separated water comprises a discharge exit disposed in said second bowl end portion.
 7. A decanting centrifuge as claimed in claim 5 wherein said bowl and said drum are disposed so that a space is provided therebetween, and said means for removing sewage sludge comprises a second helical conveyor secured to said rotary drum and disposed in said space between said rotary drum and said bowl, said second helical conveyor being pitched to guide the sewage sludge in a direction opposite to that of said first helical conveyor.
 8. A decanting centrifuge as claimed in claim 7 wherein said means for removing sewage sludge further comprises a discharge exit disposed between the tapered surfaces of said first drum end portion and said first bowl end portion at the points of smallest diameter of said respective end portions. 